In sound reproduction and in scientific instruments there is a need for mechanical elements that rotate with extreme uniformity of speed and freedom from side play and other such disturbances. High-fidelity phonograph turntables have particularly stringent requirements. In an ordinary 331/3 rpm "LP" disc record, the maximum recording amplitude or groove displacement is about 0.0023 cm. From a frequency of about 1 KHz down to about 40 Hz, this maximum remains the same; the output of a magnetic phonograph pickup varies, however, directly with frequency so that the electrical signal at 40 Hz is about 1/25 that at 1 KHz. Hence, in practice, the signal is equalized electrically, the amplifier gain being about 25 times greater at 40 Hz than at 1 KHz. Thus, the effect of a given mechanical disturbance of the turntable is 25 times greater at the lower frequency: a disturbance of 0.0023/25 or about 10.sup.-4 cm at 40 Hz produces an electrical signal, after equalization, equivalent to maximum groove modulation. Assuming now a desired signal-to-noise ratio of 60 db or 1000:1, any undesired mechanical disturbance or "noise" at around 40 Hz should be less than 0.0023/(25.times.1000) cm, or about 10.sup.-7 cm. This is about 10 Angstrom units, of the order of atomic dimensions.
For phonograph turntable bearings and tape recorder capstan bearings and the like, it has been customary to use closely-fitted sleeve bearings of generally conventional design, with thrust washers or ball thrust bearings supporting the end of the shaft. Ball bearings are known to produce more noise or mechanical disturbances or irregularities than plain bearings, because the balls cannot be exactly spherical, nor the ball races precisely round.
Sleeve bearings, however, have a tendency for the shaft to wander in the bore, producing so-called turntable rumble in phonograph applications. A need still exists for a bearing that constrains a shaft to purer rotary motion with less lateral and longitudinal "noise" disturbance than heretofore.